A multi-agent System Approach for Featuredriven Generalization of isobathymetric Line - Advances in Cartography and GIScience - page 479

would allow the generalization of terrain features through contour gener-
alization.
Only isobaths are considered in this paper as they are the main elements
characterizing the relief. The constraints will be considered to maintain the
shape of isobaths and features. Although other elements such as soundings
are not considered, the model can be easily extended so as to include these
elements in future work.
The objective of this paper is to present a model for isobath generalization
that can deal with constraints specific to nautical charts. A multi agent sys-
tem model is presented where agents model not only the lines but also the
features so that terrain information is considered in the process. In the next
section, constraints specific to nautical chart generalization are reviewed
together with related works on isobath generalization. Following section
discusses related works on multi-agent based generalization. Then, the
generalization strategy is presented, including the feature description and
the agent model. Finally, conclusions and perspectives for future studies
are presented.
2- Generalization constraints on nautical charts
Referring to Ruas and Plazanet (1997) classification, the main constraints
in isobath generalization for nautical chart are classified as:
• The legibility constraint: generalized lines must be clearly legible and a
minimal distance must be observed between them. Polygonal lines must
be of a sufficiently big area to be visible and contain a sounding;
• The functional constraint: it is related to navigation safety and states
that the generalized representation of the relief must be higher than the
original representation so that the depth interpreted from the chart can-
not be deeper than the real depth. A line cannot be deleted if it models
an upper section of the relief on the seabed ( Figure 1 ). A deformation
can only be done if the isobathymetric line is pushed towards bigger
depth. This implies that usual operators for smoothing or displacement
cannot be applied and that specific operations are used;
• The structural and shape constraints: morphological details of the sea-
floor (slope, roughness) must be maintained as much as possible. Char-
acteristic features of the relief must be maintained and emphasized;